The present invention relates to a new and improved arrangement for regulating a rolling mill, particularly a so-called four-high rolling mill for the rolling of metal.
Generally speaking, the four-high rolling mill for metal rolling is of the type whose work rolls are supported by the guided, usually cam-guided, roll shells of a lower controlled deflection roll and an upper controlled deflection roll. The roll shells are supported by means of hydrostatic pressure or support elements upon a related roll or support beam.
Such type of rolling mill has been described and illustrated in German Patent Publication No. 2,507,233 and the corresponding U.S. Pat. No. 4,509,976, granted Nov. 29, 1977, without any specific reference being made however to the rolling of metals.
For the rolling of metals this arrangement with two cam-guided, that is to say, so-called "floating" roll shells, in other words roll shells which are not fixed at their ends by bearings in their vertical direction, is preferred because there is thereby realized a large number of degrees of freedom of movement.
What is ultimately strived for during metal rolling is a specific reduction in the thickness of the rolled material or stock. Therefore, it would be obvious to measure the thickness of the rolled material following the roll gap or nip and, as a function of the deviations of the measured actual value from a predetermined reference or set value, to act upon those elements which affect the rolling operation. In the case of a rolling mill of the above-described type it is therefore necessary to act upon the hydrostatic pressure or support elements.
However, such technique is associated with appreciable difficulties. Firstly, it is impossible to avoid that appreciable delays in time are associated with the measurement of the thickness of the rolled material or stock, because the conventional throughflow rate thickness-measuring devices output an irregular pulse train which must be meaned or averaged as a function of time. Additionally, the roll shells are advantageously supported by a multiplicity of independently controllable pressure elements, so that the force exerted by the individual pressure or support elements or pressure elements connected together into groups, upon the related roll shell can be individually adjusted. In such case it would be possible to operatively associate, as taught in German Patent Publication No. 2,555,677 and the corresponding U.S. Pat. No. 4,074,624, granted Feb. 21, 1978, with each such group of pressure or support elements its own thickness measuring device and to construct a correspondingly large number of parallel regulation circuits. Yet, the equipment expenditure with this system design, particularly for metal rolling mills, would be hardly justifiable. Moreover, there would still remain unsolved the problem of controlling the regulation operation as a function of time.
A further aspect during the design of a regulation system for rolling mills of the type here under discussion pertains to the economies of the system. It will be appreciated that the specifications for the rolling operation appreciably differ depending upon the rolled product, for instance there play a role such factors as the nature of the material from which the product to be rolled is formed, such as whether it is formed of steel, aluminium, the hardness of the material, the work speed and so forth. With a direct regulation as above-described it would be necessary to provide for each individual field of use or application a specially constructed or "tailored" regulation arrangement. Obviously, this would entail a correspondingly expensive development and construction work for each individually encountered situation, even if the mechanical components or parts of the system, such as the work rolls and the back-up or support rolls, essentially remain unchanged in their design or construction.